In 1986, friends Billie Joe Armstrong and Mike Dirnt, 14 years old at the time, formed a band called Sweet Children. Their first live performance took place on October 17, 1987, at Rod's Hickory Pit in Vallejo, California. In 1988, Armstrong and Dirnt began working with former Isocracy drummer John Kiffmeyer, also known as "Al Sobrante". Hughes left the band in 1988, and Dirnt took over on bass duties. As said in the film Punk's Not Dead, Armstrong cites the band Operation Ivy (which featured Tim Armstrong and Matt Freeman of Rancid) as a major influence, and a group that inspired him to form a band.
In 1988, Larry Livermore, owner of Lookout! Records, saw the band play an early show and signed the group to his label. In 1989, the band recorded its debut extended play, 1,000 Hours. Before 1,000 Hours was released, the group dropped the name Sweet Children; according to Livermore, this was done to avoid confusion with another local band Sweet Baby. The band adopted the name Green Day, due to their fondness for cannabis.